Fuel consumption query

Mr_Sukebe

Mr_Sukebe

Mr_Sukebe

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Here's a query for you chaps.
Imagine a standard car (e.g. Fox's bimmer). In this scenario it will start from parked and travel one mile. We have two options:
1. The car is gradually accelerated in a linear fashion, so that just as the car hit's the one mile mark, it's travelling at 60mph.
2. The car is accelerated as fast as possible to 60mph, and then coasts along at that speed for the rest of the mile.

Just to recap, the cars have travelled the same distance, and accelerated by the same overall amount.
From standard physics Force = Mass * Acceleration
Quite clearly, there's no mention of time in there.

So which is the most fuel efficient? Have to say that I don't know the answer

Another few variables that I did think of were:
- Rolling resistance of the car
- transmission losses
- drag facter
- the efficiency of the engine, which will vary depending upon the revs at the time.

Any thoughts?
 
I would say the quick acceleration is better, that way you spend less time at higher speed, ergo less air resistance. So long as the car can roll for 1 mile minus the distance required to reach 60.

You don't live 1 mile from work on a national limit road do you?
 
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There is time in there as a component of acceleration. Accerating quickly is the most efficent option.
 
1. Will be more fuel efficient, accelerating hard uses lots of fuel, more than you would gain back by any amount of coasting unless you were going down a very long hill.
 
Going from personal experience, a decent rate (i.e not absolutely gunning it, but certainly not holding anyone up) of acceleration followed by coasting and/or maintaining speed is more economical than accelerating slowly. Plus its a lot less annoying.
 
Mr_Sukebe said:
Here's a query for you chaps.
Imagine a standard car (e.g. Fox's bimmer). In this scenario it will start from parked and travel one mile. We have two options:
1. The car is gradually accelerated in a linear fashion, so that just as the car hit's the one mile mark, it's travelling at 60mph.
2. The car is accelerated as fast as possible to 60mph, and then coasts along at that speed for the rest of the mile.

Just to recap, the cars have travelled the same distance, and accelerated by the same overall amount.
From standard physics Force = Mass * Acceleration
Quite clearly, there's no mention of time in there.

So which is the most fuel efficient? Have to say that I don't know the answer

Another few variables that I did think of were:
- Rolling resistance of the car
- transmission losses
- drag facter
- the efficiency of the engine, which will vary depending upon the revs at the time.

Any thoughts?
Click to expand...
Accelerating 'briskly' but not nailing it though the gears is best because the engine is most efficient when the throttle is 3/4 - fully open (so i read)
 
Gentle use of the right pedal, every time.

This makes a HUGE difference with an HGV I can tell you.
 
lordrobs said:
Are we assuming a warm engine? Hard acceleration plus cold engine = drinking fuel
Click to expand...

Either mate, gentle light use of the throttle will reap big improvements in MPG hot or cold.
 
I would imagine #1 would be most economical.
Drag increases exponentially at speed plus ragging it through the lower gears (on a cold engine where it is likely the ECU will be dumping more fuel in anyway to compensate) you can almost watch the fuel needle dropping :)

I'm gonna keep telling myself it's #2 though because I enjoy it more :p
 
Other than 'absolutely ruins it' what do you guys reckon a mile down a road with speedramps requiring the car to come to a virtual standstill to negotiate with a stone cold engine does to your fuel economy :(
 
[TW]Fox said:
surely 3 seconds acceleration followed by 57 seconds cruise is better than 30 seconds acceleration and 30 seconds cruise.
Click to expand...

I guess that essentially both methods use the same amount of fuel.....the former method is probs the most fun tho ;)
 
[TW]Fox said:
Other than 'absolutely ruins it'
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Think you basically summed it up :p

Random fuel economy rambling- I'm wondering just how accurate trip computers are because if the one in my car and the courtesy car I've currently got are correct then driving through town in my Octavia gives a whopping 2mpg less than a 1.2 Roomster, and over a bit of town and a bit of rural (30's and 40's) driving they are actually almost identical :confused: Then again being a courtesy car its probably broken :p

EDIT- actually according to the RAC its a 1.4 :o
 
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Accelerating slowly most likely.

Full throttle will run rich meaning an excess of fuel in combustion. Also full throttle will more than likely mean higher engine revs, increasing friction in the engine.
 
Quickly go thru the gears without flooring it and coasting in fifth the rest of the way is best.

running the car in first and second while accelerating uses a lot of fuel, accelerating briskly uses a bit more but the time spent doing that is much shorter.
 
BigglesPiP said:
I would say the quick acceleration is better, that way you spend less time at higher speed, ergo less air resistance.
Click to expand...

How do you work that out? If you accelerate quickly, you reach your cruising speed more quickly, and hence spend MORE time at higher speed.
 
Dogbreath said:
How do you work that out? If you accelerate quickly, you reach your cruising speed more quickly, and hence spend MORE time at higher speed.
Click to expand...
60mph in 5th gear uses a lot less fuel than 25mph in 2nd
 
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